HETEROGENEITY OF EPIDERMAL GROWTH-FACTOR BINDING-KINETICS ON INDIVIDUAL CELLS

Binding of fluorescein-conjugated epidermal growth factor (EGF) to ind ividual A431 cells at 4 degrees C is measured by a quantitative fluore scence imaging technique. After background fluorescence and cell autof luorescence photobleaching corrections, the kinetic data are fit to si mple models of one monovalent site and two independent monovalent site s, both of which include a first-order dye photobleaching process. Mod el simulations and the results from data analysis indicate that the on e-monovalent-site model does not describe EGF binding kinetics at the single-cell level, whereas the two-site model is consistent with, but not proved by, the single-cell binding data. In addition, the kinetics of binding of fluorescein-EGF to different cells from the same covers lip often differ significantly from each other, indicating cell-to-cel l variations in the binding properties of the EGF receptor.